Semiconductor structure

ABSTRACT

A semiconductor structure includes a conductive line, a pad layer, and a barrier layer. The conductive line is embedded in a multi-level interconnect structure. The pad layer is over the conductive line. The barrier layer is between the conductive line and the pad layer. The pad layer is electrically connected to the conductive line through the barrier layer, and the barrier layer includes a first poly-crystalline layer and a second poly-crystalline layer. A boundary is between the first poly-crystalline layer and the second poly-crystalline layer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation application of the U.S. application Ser. No. 17/160,251, filed Jan. 27, 2021, now U.S. Pat. No. 11,515,256, issued on Nov. 29, 2022, which is hereby incorporated by reference in its entirety.

BACKGROUND

A semiconductor device includes one or numerous conductive metal layers serving as metal interconnect. The conductive metal layers couple various device components to one another through dielectric materials. The conductive metal layers are formed over one another and positioned at various device levels. Further, the semiconductor device includes an uppermost or top metal layer serving as a part of a pad structure. Hence, the top metal layer may electrically couple a solder bump or other external component, so as to enable electrical connection to the semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1-9B illustrate a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

FIG. 10 is an enlarged view of the area B′ in FIG. 9A in accordance with some embodiments of the present disclosure.

FIG. 11 is a flow chart of a method for forming a semiconductor structure in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

As used herein, “around”, “about”, “approximately”, or “substantially” shall generally mean within 20 percent, or within 10 percent, or within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about”, “approximately”, or “substantially” can be inferred if not expressly stated.

Some embodiments of the present disclosure relate to semiconductor structures having multiple barrier layers to prevent metal from diffusion. With such configurations, metal elements of conductive lines underlying the barrier layers are not easy to pass through all of the multiple barrier layers, and the performance of the barrier layer is enhanced.

FIGS. 1-9B illustrate a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure. In some embodiments, the semiconductor device shown in FIGS. 1-9B may be intermediate devices fabricated during processing of an integrated circuit (IC), or a portion thereof, that may include static random access memory (SRAM), logic circuits, passive components, such as resistors, capacitors, and inductors, and/or active components, such as p-type field effect transistors (PFETs), n-type FETs (NFETs), multi-gate FETs, metal-oxide semiconductor field effect transistors (MOSFETs), complementary metal-oxide semiconductor (CMOS) transistors, bipolar transistors, high voltage transistors, high frequency transistors, other memory cells, and combinations thereof.

Reference is made to FIG. 1 . A substrate 110 is provided. In some embodiments, the substrate 110 may include silicon (Si). Alternatively, the substrate 110 may include germanium (Ge), silicon germanium (SiGe), gallium arsenide (GaAs) or other appropriate semiconductor materials. In some embodiments, the substrate 110 may include a semiconductor-on-insulator (SOI) structure such as a buried dielectric layer. Also alternatively, the substrate 110 may include a buried dielectric layer such as a buried oxide (BOX) layer, such as that formed by a method referred to as separation by implantation of oxygen (SIMOX) technology, wafer bonding, SEG, or another appropriate method. In various embodiments, the substrate 110 may include any of a variety of substrate structures and materials.

In some embodiments, a plurality of isolation features 120, such as shallow trench isolation (STI) features or local oxidation of silicon (LOCOS) features, are formed in the substrate 110. The isolation features 120 may define and isolate active regions for various microelectronic elements, such as transistors (metal oxide semiconductor field effect transistor (MOSFET), complementary metal oxide semiconductor (CMOS) transistor, bipolar junction transistor (BJT), high voltage transistor, high frequency transistor, etc.), resistors, diodes, capacitors, and other suitable elements. Accordingly, various processes are performed such as deposition, etching, implantation, photolithography, annealing, and other suitable processes that are available to one of ordinary skill in the art to form the microelectronic elements. The microelectronic elements are interconnected to form an integrated circuit such as a logic device, memory device (e.g., SRAM), RF device, input/output (I/O) device, system-on-chip (SoC) device, combinations thereof, and other suitable type of devices known in the art.

An interlayer dielectric (ILD) 130 is formed over the substrate 110 including the microelectronic elements. The ILD 130 may include silicon oxide, silicon oxynitride, or a low-k material. The ILD 130 may be formed by chemical vapor deposition (CVD), high density plasma CVD (HDP-CVD), spin-on, physical vapor deposition (PVD or sputtering), or other suitable technique. It should be noted a stressed layer such as a contact etch stop layer (CESL) may be formed over the substrate 110 prior to forming the ILD 130.

In some embodiments, a plurality of contacts 140 are formed in the ILD 130. The contacts 140 may be formed by patterning and etching the ILD 130 to form trenches. The trenches may be filled by depositing a metal barrier layer such as TiN, and then depositing a contact plug layer such as W on the metal barrier layer. In some embodiments, the metal barrier layer may include Ti/TiN for a W contact plug. In some other embodiments, the metal barrier layer may include Ta/TaN for a Cu contact plug. The contacts 140 provide connections to the various microelectronic elements formed in the substrate 110.

A multi-level interconnect structure 150 is formed above the ILD 130 and the contacts 140. The multi-level interconnect structure 150 includes a plurality of conductive layers 150 a-150 g that provide interconnections (wiring) between the various microelectronic elements, and between conductive layers themselves. It is understood that the number of conductive layers may vary depending on the design of the particular semiconductor device. In FIG. 1 , the conductive layers 150 a-150 g include seven (7) conductive layers with a bottommost conductive layer 150 a (M1), a topmost conductive layer 150 g (M7), and conductive layers 150 b-150 f (M2-M6) between the bottommost conductive layer 150 a and topmost conductive layer 150 g. The conductive layers 150 a-150 g (M1-M7) may include lines formed of a conductive material such as aluminum, aluminum/silicon/copper alloy, titanium, titanium nitride, tungsten, polysilicon, metal silicide, or combinations thereof. Alternatively, the conductive layers 150 a-150 g may include lines formed of copper, copper alloy, titanium, titanium nitride, tantalum, tantalum nitride, tungsten, polysilicon, metal silicide, or combinations thereof.

The conductive layers 150 a-150 g (M1-M7) may be insulated from each other by inter-metal dielectric (IMD) layers 160. The IMD layers 160 may include a material of a low dielectric constant or low k value (low-k). In some embodiments, the IMD layers 160 at various levels of the multi-level interconnect structure 150 may be formed of different dielectric materials. It is has been observed that IMD layers 160 with low-K (LK), extreme low-K (ELK), and/or extra low-k (XLK) materials may enhance circuit performance. The material classification may be based upon a dielectric constant. For example, LK materials may refer to those materials with a k value less than approximately 3.5, and preferably less than approximately 3.0. The ELK materials may refer to those materials with a k value less than approximately 2.9, and preferably less than approximately 2.6. The XLK materials may refer to those materials which typically have a k value less than approximately 2.4. It is understood that the classifications are mere examples and that other classifications based on the dielectric constant of the material may be utilized as well. The LK, ELK, and/or XLK dielectric materials may include silicon nitride, silicon oxynitride, spin-on glass (SOG), undoped silicate glass (USG), fluorinated silica glass (FSG), carbon doped silicon oxide (e.g., SiCOH), carbon-containing material, Black Diamond® (Applied Materials of Santa Clara, Calif.), Xerogel, Aerogel, amorphous fluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), Flare, SiLK (Dow Chemical, Midland, Mich.), polyimide, other proper porous polymeric materials, other suitable dielectric materials, and/or combinations thereof. The IMD layers 160 may be formed by a technique including spin-on, CVD, PVD, or atomic layer deposition (ALD).

The conductive layers 150 a-150 g and the IMD layers 160 may be formed in an integrated process such as a damascene process or lithography/plasma etching process. The bottommost conductive layer 150 a (M1) may include conductive lines 152 that are coupled to the contacts 140 for connecting to the microelectronic elements formed in the substrate 110. The multi-level interconnect structure 150 may further include various metal vias 165 disposed within the IMD layers 160 for connecting the conductive lines 152 of adjacent conductive layers 150 a-150 g.

Reference is made to FIG. 2 . An etch stop layer (ESL) 210 is formed above the conductive layers 150 a-150 g (M1-M7) and the IMD layers 160. In some embodiments, the ESL 210 provides a mechanism to stop an etching process when forming vias and/or contacts. The ESL 210 is formed of a dielectric material having a different etch selectivity from adjacent layers, e.g., the underlying conductive layer 150 g. In some embodiments, the ESL 210 may be formed of SiNx, SiCN, SiO₂, CN, AlO_(x)N_(y), combinations thereof, or the like, deposited by CVD or PECVD techniques.

Subsequently, a first passivation layer 220 is formed above the ESL 210. The first passivation layer 220 may be made of non-organic material selected from un-doped silicate glass (USG), silicon nitride, silicon oxynitride, silicon oxide, and/or multi-layers thereof. Alternatively, the first passivation layer 220 may be made of a polymer layer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used. In some embodiments, a thickness of the first passivation layer 220 is greater than a thickness of the ESL 210.

A first photoresist layer 310 with an opening 312 is formed above the first passivation layer 220. The first photoresist layer 310 is formed by spin-on coating or other suitable technique. Other operations, such as baking, may follow the coating of the first photoresist layer 310. In some embodiments, the opening 312 exposes a portion of the first passivation layer 220 directly above one of the conductive lines 152 in the topmost conductive layer 150 g (M7).

Reference is made to FIGS. 3A and 3B, where FIG. 3B is an enlarged view of area B in FIG. 3A. An opening 222 is formed in the first passivation layer 220 and the ESL 210 to expose a portion of the conductive line 152 in the topmost conductive layer 150 g (M7). The portions of the first passivation layer 220 and the ESL 210 are removed based on the patterned photoresist layer 310 (see FIG. 2 ) to form the opening 222, and the patterned photoresist layer 310 is removed after the formation of the opening 222. In some embodiments, the opening 222 includes a bottom 222 b (i.e., the top surface of the corresponding conductive line 152) and sidewalls 222 s (i.e., the inner sidewalls of the first passivation layer 220).

Reference is made to FIG. 4 . A barrier layer 230 (see FIG. 5 ) is conformally formed above the structure of FIG. 3A. That is, the barrier layer 230 lines the inner sidewalls 222 s of the first passivation layer 220, a top surface 220 t of the first passivation layer 220, and the top surface 222 b of the conductive line 152. The barrier layer 230 may function as a barrier to prevent metal elements of the conductive line 152 from diffusing to the subsequently formed pad layer 240 (see FIG. 7 ) and/or prevent metal elements of the subsequently formed pad layer 240 from diffusing into the first passivation layer 220. Specifically, a first bottom layer 232 a is deposited covering the sidewalls 222 s and the bottom 222 b of the opening 222. That is, the first bottom layer 232 a is conformally formed in the opening 222. By forming the first bottom layer 232 a conformally, the first bottom layer 232 a will have a substantially equal thickness along the sidewalls 222 s of the opening 222 and also along the bottom 222 b of the opening 222. The first bottom layer 232 a may be formed using a process such as chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced CVD (PECVD), plasma enhanced physical vapor deposition (PEPVD), atomic layer deposition (ALD), combinations of these, or the like.

In some embodiments, the first bottom layer 232 a is made of tantalum, titanium, combinations thereof, or the like. In some embodiments, the first bottom layer 232 a is a metal layer. In some other embodiments, the first bottom layer 232 a is a pure metal layer or a substantially pure metal layer, for example, with a metal percentage higher than about 99 percent. In some embodiments, the first bottom layer 232 a is a nano-crystalline phase (very small crystals or grains, close to amorphous). In some embodiments, the first bottom layer 232 a has a thickness T1 a in a range of about 20 angstrom to about 30 angstrom. In some embodiments, the first bottom layer 232 a is formed by PVD techniques using a source DC power in a range of about 475 kW to about 525 kW.

Next, a first middle layer 234 a is conformally formed above the first bottom layer 232 a. By forming the first middle layer 234 a conformally, the first middle layer 234 a will have a substantially equal thickness along the sidewalls 222 s of the opening 222 and also along the bottom 222 b of the opening 222. The first middle layer 234 a may be formed using a process that will promote a conformal formation, such as atomic layer deposition (ALD). Other processes such as plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced physical vapor deposition (PEPVD), wherein a bias is applied to the substrate 110 in order to lessen variations in the thickness of the first middle layer 234 a, may alternatively be used. In some embodiments, the first middle layer 234 a is formed by PVD techniques using a source DC power in a range of about 475 kW to about 525 kW. In some embodiments, the first bottom layer 232 a and the first middle layer 234 a are formed with substantially the same power (e.g., about 500 W).

In some embodiments, the first middle layer 234 a is made of tantalum nitride, titanium nitride, combinations thereof, or the like. In some embodiments, the first middle layer 234 a is a nitride layer. In some embodiments, a metal percentage of the first middle layer 234 a is lower than the metal percentage of the first bottom layer 232 a. In some embodiments, the first middle layer 234 a is an amorphous phase. In some embodiments, the first middle layer 234 a has a thickness T2 a in a range of about 18 angstrom to about 22 angstrom. In some embodiments, the thickness T2 a is greater than, less than, or substantially the same as the thickness T1 a of the first bottom layer 232 a.

Subsequently, a first top layer 236 a is conformally formed above the first middle layer 234 a. By forming the first top layer 236 a conformally, the first top layer 236 a will have a substantially equal thickness along the sidewalls 222 s of the opening 222 and also along the bottom 222 b of the opening 222. The first top layer 236 a may be formed using a process that will promote a conformal formation, such as atomic layer deposition (ALD). Other processes such as plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced physical vapor deposition (PEPVD), wherein a bias is applied to the substrate in order to lessen variations in the thickness of the first top layer 236 a, may alternatively be used. In some embodiments, the first top layer 236 a is formed by PVD techniques using a source DC power in a range of about 5700 kW to about 6300 kW. In some embodiments, the first top layer 236 a is formed with a power higher than that of the first middle layer 234 a for greater than about ten times.

In some embodiments, the first top layer 236 a is made of tantalum nitride, titanium nitride, combinations thereof, or the like. In some embodiments, the first top layer 236 a is a nitride layer. In some embodiments, a metal percentage of the first top layer 236 a is lower than the metal percentage of the first bottom layer 232 a. In some embodiments, the first top layer 236 a is a poly-crystalline phase. In some embodiments, the first top layer 236 a has a thickness T3 a in a range of about 170 angstrom to about 190 angstrom. In some embodiments, the thickness T3 a is greater than the thickness T2 a of the first middle layer 234 a. In some embodiments, the thickness T3 a of the first top layer 236 a is greater than the thickness T1 a of the first bottom layer 232 a. In FIG. 4 , the first bottom layer 232 a, the first middle layer 234 a, and the first top layer 236 a are together referred to as a first barrier layer 230 a.

Reference is made to FIG. 5 . A second barrier layer 230 b of the barrier layer 230 is conformally formed above the first barrier layer 230 a. The second barrier layer 230 b includes a second bottom layer 232 b, a second middle layer 234 b, and a second top layer 236 b. The formation and the material of the second bottom layer 232 b are similar to or the same as the formation and the material of the first bottom layer 232 a, and, therefore, a description in this regard will not be repeated hereinafter. The formation and the material of the second middle layer 234 b are similar to or the same as the formation and the material of the first middle layer 234 a, and, therefore, a description in this regard will not be repeated hereinafter. The formation and the material of the second top layer 236 b are similar to or the same as the formation and the material of the first top layer 236 a, and, therefore, a description in this regard will not be repeated hereinafter.

Subsequently, a third barrier layer 230 c of the barrier layer 230 is conformally formed above the second barrier layer 230 b. The third barrier layer 230 c includes a third bottom layer 232 c, a third middle layer 234 c, and a third top layer 236 c. The formation and the material of the third bottom layer 232 c is similar to or the same as the formation and the material of the first bottom layer 232 a, and, therefore, a description in this regard will not be repeated hereinafter. The formation and the material of the third middle layer 234 c is similar to or the same as the formation and the material of the first middle layer 234 a, and, therefore, a description in this regard will not be repeated hereinafter. The formation and the material of the third top layer 236 c is similar to or the same as the formation and the material of the first top layer 236 a, and, therefore, a description in this regard will not be repeated hereinafter. As such, the first barrier layer 230 a, the second barrier layer 230 b, and the third barrier layer 230 c are together referred to as the barrier layer 230.

Reference is made to FIG. 6 . Next, a conductive material 240′ is formed above the barrier layer 230 and fills the remaining space of the opening 222. For clarity, the sub-layers (i.e., the layers shown in FIG. 5 ) of the barrier layer 230 are not shown in FIG. 6 . In some embodiments, the conductive material 240′ is a metal layer and may include aluminum (Al), although it may also be made of copper (Cu), silver (Ag), gold (Au), nickel (Ni), tungsten (W), alloys, or any combination thereof. In some other embodiments, the conductive material 240′ may be made of aluminum copper (AlCu). In some embodiments, the conductive material 240′ is made by using sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical copper plating (ECP), and the like.

Subsequently, an antireflective coating layer 245′ is formed above the conductive material 240′. The antireflective coating layer 245′ may be formed over the conductive material 240′ to aid in a subsequent photolithographic process to pattern an overlying layer. The antireflective coating layer 245′ prevents radiation in a subsequent photolithographic process to reflect off layers below and interfere with the exposure process. Such interference can increase the critical dimension of the photolithography process. The antireflective coating layer 245′ may include SiON, a polymer, the like, or combinations thereof and may be formed by CVD, a spin-on process, the like, or combinations thereof. In some embodiments, the antireflective coating layer 245′ is formed under a high temperature, e.g., greater than about 300 degrees Celsius, and the barrier layer 230 can prevent the metal elements in the conductive lines from passing through the barrier layer 230 and the conductive material 240′ during the high temperature process for forming the antireflective coating layer 245′. The antireflective coating layer 245′ has a thickness sufficient to provide sufficient antireflective qualities based upon the materials and the wavelength.

A second photoresist layer 320 is formed above the antireflective coating layer 245′. The second photoresist layer 320 is formed by spin-on coating or other suitable technique. Other operations, such as baking, may follow the coating of the second photoresist layer 320. The second photoresist layer 320 is formed directly above the opening 222, and portions of the antireflective coating layer 245′ are uncovered by the second photoresist layer 320.

Reference is made to FIG. 7 . The antireflective coating layer 245′, the conductive material 240′, and the barrier layer 230 are patterned using the second photoresist layer 320 (see FIG. 6 ) as a mask to form an antireflective coating layer 245, a pad layer 240, and a barrier layer 230 in the opening and above the first passivation layer 220, and the second photoresist layer 320 is removed.

Reference is made to FIG. 8 . A second passivation layer 250 is formed above the structure in FIG. 7 . The formation and material of the second passivation layer 250 are similar to or the same as the formation and the material of the first passivation layer 220, and, therefore, a description in this regard will not be repeated hereinafter. Subsequently, a third passivation layer 260 is formed above the second passivation layer 250. The formation and material of the third passivation layer 260 are similar to or the same as the formation and the material of the ESL 210, and, therefore, a description in this regard will not be repeated hereinafter.

Reference is made to FIGS. 9A and 9B, where FIG. 9B is an enlarged view of area B′ in FIG. 9A. A patterning process is performed on the second passivation layer 250 and third passivation layer 260, such that an opening 265 is formed in the second passivation layer 250 and third passivation layer 260 to expose a top surface of the antireflective coating layer 245. For example, another patterned photoresist is formed above the third passivation layer 260, and an etching process is performed to remove portions of the second passivation layer 250 and third passivation layer 260 exposed by the patterned photoresist. The patterned photoresist is then removed after the etching process.

A semiconductor structure shown in FIGS. 9A and 9B includes the multi-level interconnect structure 150, the first passivation layer 220, the barrier layer 230, and the pad layer 240. The first passivation layer 220 is above the multi-level interconnect structure 150 and exposes portions of the conductive line 152. The barrier layer 230 is conformally formed above the first passivation layer 220 and the conductive line 152. The pad layer 240 is above the barrier layer 230, such that the pad layer 240 can be electrically connected to the conductive line 152 through the barrier layer 230.

The barrier layer 230 includes the first barrier layer 230 a, the second barrier layer 230 b, and the third barrier layer 230 c. The second barrier layer 230 b is above the first barrier layer 230 a, and the third barrier layer 230 c is above the second barrier layer 230 b. That is, the second barrier layer 230 b is sandwiched between (and in directly contact with) the first barrier layer 230 a and the third barrier layer 230 c. The first barrier layer 230 a is sandwiched between (and in directly contact with) the conductive line 152 (or the first passivation layer 220) and the second barrier layer 230 b. The third barrier layer 230 c is sandwiched between (and in directly contact with) the second barrier layer 230 b and the pad layer 240.

The first barrier layer 230 a includes the first bottom layer 232 a, the first middle layer 234 a, and the first top layer 236 a. The second barrier layer 230 b includes the second bottom layer 232 b, the second middle layer 234 b, and the second top layer 236 b. The third barrier layer 230 c includes the third bottom layer 232 c, the third middle layer 234 c, and the third top layer 236 c.

In some embodiments, each of the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c is made of tantalum, titanium, combinations thereof, or the like. In some embodiments, each of the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c is a metal layer and free from nitrogen. In some other embodiments, each of the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c is a pure metal layer or a substantially pure metal layer, for example, with a metal percentage higher than about 99 percent. In some embodiments, each of the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c is a nano-crystalline phase (very small crystals or grains, close to amorphous). In some embodiments, each of the thickness T1 a of the first bottom layer 232 a, the thickness T1 b of the second bottom layer 232 b, and the thickness T1 c of the third bottom layer 232 c is a in a range of about 20 angstrom to about 30 angstrom. In some embodiments, the thickness T1 a is greater than, equal to, or less than the thickness T1 b (or T1 c).

In some embodiments, each of the first middle layer 234 a, the second middle layer 234 b, and the third middle layer 234 c is made of tantalum nitride, titanium nitride, combinations thereof, or the like. In some embodiments, each of the first middle layer 234 a, the second middle layer 234 b, and the third middle layer 234 c is a nitride layer and has a higher nitrogen concentration than that of each of the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c. In some embodiments, a metal percentage of each of the first middle layer 234 a, the second middle layer 234 b, and the third middle layer 234 c is lower than the metal percentage of the first bottom layer 232 a. In some embodiments, each of the first middle layer 234 a, the second middle layer 234 b, and the third middle layer 234 c is an amorphous phase. In some embodiments, each of the thickness T2 a of the first middle layer 234 a, the thickness T2 b of the second middle layer 234 b, and the thickness T2 c of the third middle layer 234 c in a range of about 18 angstrom to about 22 angstrom. In some embodiments, the thickness T2 a is greater than, equal to, or less than the thickness T2 b (or T2 c).

In some embodiments, each of the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c is made of tantalum nitride, titanium nitride, combinations thereof, or the like. In some embodiments, each of the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c is a nitride layer and has a higher nitrogen concentration than that of each of the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c. In some embodiments, a metal percentage of each of the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c is lower than the metal percentage of the first bottom layer 232 a. In some embodiments, each of the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c is a poly-crystalline phase. In some embodiments, each of the thickness T3 a of the first top layer 236 a, the thickness T3 b of the second top layer 236 b, and the thickness T3 c of the third top layer 236 c is in a range of about 170 angstrom to about 190 angstrom. In some embodiments, the thickness T3 a is greater than, equal to, or less than the thickness T3 b (or T3 c).

In some embodiments, the first bottom layer 232 a, the first middle layer 234 a, and the first top layer 236 a include the same metal (e.g., tantalum). In some embodiments, the second bottom layer 232 b, the second middle layer 234 b, and the second top layer 236 b include the same metal (e.g., tantalum). In some embodiments, the third bottom layer 232 c, the third middle layer 234 c, and the third top layer 236 c include the same metal (e.g., tantalum). In some embodiments, the barrier layer 230 has a thickness T in a range of about 624 angstrom to about 726 angstrom. If the thickness T is greater than about 726 angstrom, the barrier layer 230 may have high resistance; if the thickness T is less than about 624 angstrom, the electrical performance of the barrier layer 230 may be undesirable. In some embodiments, a ratio of T2 a:T3 a is in a range of about 0.094 and about 0.129. If the ratio of T2 a:T3 a is out of this range, the barrier layer 230 may not meet the desired electrical performance of the semiconductor device. In some embodiments, a sum of the thicknesses T1 a, T2 a, and T3 a is in a range of about 208 angstrom and about 242 angstrom. If the sum of the thicknesses T1 a, T2 a, and T3 a is greater than about 242 angstrom, the barrier layer 230 may have high resistance; if the sum of the thicknesses T1 a, T2 a, and T3 a is less than about 208 angstrom, the electrical performance of the barrier layer 230 may be undesirable. In some embodiments, the ratio of T1 a:T2 a:T3 a is substantially equal to the ratio of T1 b:T2 b:T3 b and substantially equal to the ratio of T1 c:T2 c:T3 c. As such, the electrical performance of the pad layer 240 is improved. In some embodiments, the ratio of T1 a:T2 a:T3 a may be in a range of about 1.2:1:8.5 to about 1.3:1:9.5, e.g., about 1.25:1:9. If the ratio of T1 a:T2 a:T3 a is out of this range, the barrier layer 230 may not meet the desired electrical performance of the semiconductor device.

As shown in FIG. 9B, since the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c are in poly-crystalline phases, threading dislocation defects 238 may be formed therein. On contrary, the threading dislocation defects may not exist in the first bottom layer 232 a, the second bottom layer 232 b, and the third bottom layer 232 c since they are in nano-crystalline phases. In FIG. 9B, since the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c are formed separately, and the second bottom layer 232 b and the third bottom layer 232 c are interposed therebetween, the threading dislocation defects 238 in the first top layer 236 a, the second top layer 236 b, and the third top layer 236 c are misaligned with each other.

Metal elements in the conductive line 152 may pass through the threading dislocation defects 238 in the first top layer 236 a during a thermal process (e.g., the deposition process of the antireflective coating layer 245′ as shown in FIG. 6 ). The metal elements, however, may be blocked by the second bottom layer 232 b and the second middle layer 234 b since there is no threading dislocation defects 238 therein. Even if rare or some metal elements still pass through the second bottom layer 232 b and the second middle layer 234 b, the misaligned configuration of the threading dislocation defects 238 in the second top layer 236 b still help blocking the diffusion of the metal elements. Also, the third bottom layer 232 c, the third middle layer 234 c, and the third top layer 236 c have the same function as the second bottom layer 232 b, the second middle layer 234 b, and the second top layer 236 b. With such configuration, the fail rate of the semiconductor structure (e.g., the metal elements of the conductive line 152 diffused to the pad layer 240) is reduced to lower than about 1% in some embodiments.

In some embodiments, the semiconductor structure further includes the ESL 210 between the first passivation layer 220 and the conductive line 152 of the topmost conductive layer 150 g. The ESL 210 is in direct contact with the first bottom layer 232 a of the barrier layer 230. In some embodiments, the semiconductor structure further includes the antireflective coating layer 245 above the pad layer 240. In some embodiments, the semiconductor structure further includes the second passivation layer 250 and a third passivation layer 260. The second passivation layer 250 is above the first passivation layer 220 and the pad layer 240, and the third passivation layer 260 is above the second passivation layer 250.

FIG. 10 is an enlarged view of the area B′ in FIG. 9A in accordance with some embodiments of the present disclosure. The difference between the structures in FIGS. 10 and 9B pertains to the thicknesses of the layers in the barrier layer 230. In FIG. 10 , the thickness T3 a of the first top layer 236 a is greater than the thickness T3 b of the second top layer 236 b, and the thickness T3 b of the second top layer 236 b is greater than the thickness T3 c of the third top layer 236 c. It may be because of the deposition rate of the barrier layer 230. For example, the deposition rate of the first top layer 236 a is greater than the deposition rate of the second top layer 236 b, and the deposition rate of the second top layer 236 b is greater than the deposition rate of the third top layer 236 c. However, the ratio of T1 a:T2 a:T3 a is substantially equal to the ratio of T1 b:T2 b:T3 b and substantially equal to the ratio of T1 c:T2 c:T3 c. Other relevant structural details of the barrier layer 230 in FIG. 10 are substantially the same as or similar to the barrier layer 230 in FIG. 9B, and, therefore, a description in this regard will not be repeated hereinafter.

FIG. 11 is a flow chart of a method M for forming a semiconductor structure in accordance with some embodiments of the present disclosure. Although the method M is illustrated and/or described as a series of acts or events, it will be appreciated that the method is not limited to the illustrated ordering or acts. Thus, in some embodiments, the acts may be carried out in different orders than illustrated, and/or may be carried out concurrently. Further, in some embodiments, the illustrated acts or events may be subdivided into multiple acts or events, which may be carried out at separate times or concurrently with other acts or sub-acts. In some embodiments, some illustrated acts or events may be omitted, and other un-illustrated acts or events may be included.

At block S12, a passivation layer is formed above a conductive line. FIG. 2 illustrates a cross-sectional view of some embodiments corresponding to act in block S12. At block S14, an opening is formed in the passivation layer. FIGS. 3A and 3B illustrates cross-sectional views of some embodiments corresponding to act in block S14. At block S16, a first bottom layer, a first middle layer, and a first top layer of a barrier layer are formed in the opening of the passivation layer. FIG. 4 illustrates a cross-sectional view of some embodiments corresponding to act in block S16. At block S18, a second bottom layer, a second middle layer, and a second top layer of the barrier layer are formed above the first top layer. FIG. 5 illustrates a cross-sectional view of some embodiments corresponding to act in block S18. At block S20, a third bottom layer, a third middle layer, and a third top layer of the barrier layer are formed above the second top layer. FIG. 5 illustrates a cross-sectional view of some embodiments corresponding to act in block S20. At block S22, a conductive material is formed above the barrier layer. FIG. 6 illustrates a cross-sectional view of some embodiments corresponding to act in block S22. At block S24, the barrier layer and the conductive material are patterned. FIG. 7 illustrates a cross-sectional view of some embodiments corresponding to act in block S24.

Based on the above discussions, it can be seen that the present disclosure offers advantages. It is understood, however, that other embodiments may offer additional advantages, and not all advantages are necessarily disclosed herein, and that no particular advantage is required for all embodiments. One advantage is that the second and/or third bottom layers of the barrier layer block metal elements of the conductive line from diffuse to the pad layer. Another advantage is that the first, second, and third top layers of the barrier layer have misaligned threading dislocation defects, the metal elements are not easy to pass through all of the first, second, and third top layers. With such configuration, the fail rate of the semiconductor structure (e.g., the metal elements of the conductive line diffused to the pad layer) is reduced to lower than about 1% in some embodiments.

According to some embodiments, a semiconductor structure includes a multi-level interconnect structure, a passivation layer, a barrier layer, and a pad layer. The passivation layer is above the multi-level interconnect structure. The barrier layer lines an inner sidewall of the passivation layer, a top surface of the passivation layer and a top surface of a conductive line of the multi-level interconnect structure. The barrier layer includes a first layer, a second layer, a third layer, and a fourth layer. The first layer is in a nano-crystalline phase. The second layer is above the first layer and in an amorphous phase. The third layer is above the second layer and in a polycrystalline phase. The fourth layer is above the third layer and in a nano-crystalline phase. The pad layer is above the barrier layer.

According to some embodiments, a semiconductor structure includes a multi-level interconnect structure, a passivation layer, a pad layer, and a barrier layer. The passivation layer is above the multi-level interconnect structure. The pad layer is partially in the passivation layer and above the multi-level interconnect structure. The barrier layer is between the multi-level interconnect structure and the pad layer. The barrier layer includes a first tantalum-containing layer, a second tantalum-containing layer, and a third tantalum-containing layer. The second tantalum-containing layer is above the first tantalum-containing layer. The third tantalum-containing layer is above the second tantalum-containing layer. The first tantalum-containing layer and the third tantalum-containing layer have a higher nitrogen concentration than that of the second tantalum-containing layer, and a thickness of the second tantalum-containing layer is less than a thickness of the third tantalum-containing layer.

According to some embodiments, a method for manufacturing a semiconductor structure including forming a passivation layer above a conductive line. An opening is formed in the passivation layer to expose the conductive line. A barrier layer is formed in the opening of the passivation layer. The formation of the barrier layer includes forming a first layer in a nano-crystalline phase. A second layer is formed above the first layer and in an amorphous phase. A third layer is formed above the second layer and in a polycrystalline phase. A fourth layer is formed above the third layer and in a nano-crystalline phase. A conductive material is formed over the barrier layer. The barrier layer and the conductive material are patterned.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor structure comprising: a conductive line embedded in a multi-level interconnect structure; a pad layer over the conductive line; and a barrier layer between the conductive line and the pad layer, wherein the pad layer is electrically connected to the conductive line through the barrier layer, and the barrier layer comprises: a first poly-crystalline layer; and a second poly-crystalline layer over the first poly-crystalline layer, wherein a boundary is between the first poly-crystalline layer and the second poly-crystalline layer.
 2. The semiconductor structure of claim 1, further comprising an amorphous layer between the first poly-crystalline layer and the second poly-crystalline layer.
 3. The semiconductor structure of claim 2, wherein the amorphous layer and the second poly-crystalline layer have substantially the same material.
 4. The semiconductor structure of claim 2, wherein the boundary is an interface between the amorphous layer and the second poly-crystalline layer.
 5. The semiconductor structure of claim 1, further comprising a nano-crystalline layer between the first poly-crystalline layer and the second poly-crystalline layer.
 6. The semiconductor structure of claim 5, wherein the first poly-crystalline layer has a nitrogen concentration higher than a nitrogen concentration of the nano-crystalline layer.
 7. The semiconductor structure of claim 1, wherein the first poly-crystalline layer and the second poly-crystalline layer are tantalum nitride layers.
 8. A semiconductor structure comprising: a multi-level interconnect structure; a passivation layer over the multi-level interconnect structure, wherein the passivation layer has a tapered inner sidewall; a pad layer over the passivation layer; and a barrier layer between the pad layer and the multi-level interconnect structure, wherein the barrier layer lines the tapered inner sidewall of the passivation layer, and the barrier layer comprises: a first layer; a second layer on and in contact with the first layer; and a third layer on and in contact with the second layer, wherein a nitrogen concentration of the second layer is lower than a nitrogen concentration of the first layer and a nitrogen concentration of the third layer, and the first layer has threading dislocation defects more than that in the third layer.
 9. The semiconductor structure of claim 8, wherein the first layer, the second layer, and the third layer comprise substantially the same metal.
 10. The semiconductor structure of claim 8, wherein the second layer is free from nitrogen.
 11. The semiconductor structure of claim 8, wherein a thickness of the first layer is greater than a thickness of the second layer.
 12. The semiconductor structure of claim 8, wherein a thickness of the first layer is greater than a thickness of the third layer.
 13. The semiconductor structure of claim 8, further comprising a fourth layer over the third layer, wherein the fourth layer and the third layer have substantially the same material.
 14. The semiconductor structure of claim 13, wherein a thickness of the first layer is greater than a thickness of the fourth layer.
 15. A semiconductor structure comprising: a conductive line over a substrate; a passivation layer over the substrate and covering the conductive line, wherein the passivation layer has an opening exposing the conductive line; a first composite barrier layer, a second composite barrier layer, and a third composite barrier layer sequentially stacked in the opening of the passivation layer, wherein each of the first composite barrier layer, the second composite barrier layer, and the third composite barrier layer comprises: a nitrogen-free metal layer; and a first nitrogen-containing metal layer over the nitrogen-free metal layer; and a pad layer over the third composite barrier layer.
 16. The semiconductor structure of claim 15, wherein each of the first composite barrier layer, the second composite barrier layer, and the third composite barrier layer further comprises: a second nitrogen-containing metal layer between the nitrogen-free metal layer and the first nitrogen-containing metal layer.
 17. The semiconductor structure of claim 16, wherein a thickness of the first nitrogen-containing metal layer is greater than a thickness of the second nitrogen-containing metal layer.
 18. The semiconductor structure of claim 15, wherein the nitrogen-free metal layer of the first composite barrier layer is in contact with the conductive line.
 19. The semiconductor structure of claim 15, wherein the first nitrogen-containing metal layer of the first composite barrier layer is in contact with the nitrogen-free metal layer of the second composite barrier layer.
 20. The semiconductor structure of claim 15, wherein the first nitrogen-containing metal layer of the first composite barrier layer is thicker than the first nitrogen-containing metal layer of the third composite barrier layer. 